Optical fiber cable with impact resistant buffer tube

ABSTRACT

An crush resistant optical cable and/or crush resistant optical fiber buffer tube are provided. The cable generally includes a tube having at least one layer formed from a first material and an optical fiber located within a channel of the first tube. The buffer tube is configured to protect optical fibers from crush or impact events through a cushioning action. For example, the first material may be a polymer material having modulus of elasticity of less than 200 MPa, and the layer of the tube acts as a compliant cushioning layer at least partially contacting and surrounding an outer surface of the optical fiber when radially directed forces are applied to the outer surface of the tube.

RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2015/045789, filed on Aug. 19, 2015, which claims the benefit ofpriority under 35 U.S.C. §119 of U.S. Provisional Application No.62/040,652, filed on Aug. 22, 2014, the content of which is relied uponand incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates generally to optical communication cables andmore particularly to optical communication cables including an opticalfiber containing tube formed from a low modulus or otherwise supportivematerial that may act to cushion and protect optical fibers duringimpact, deformation or crush events. Optical communication cables haveseen increased use in a wide variety of electronics andtelecommunications fields. Optical communication cables contain orsurround one or more optical communication fibers. The cable providesstructure and protection for the optical fibers within the cable. Withina cable, optical fibers may be located within a polymer tube, such as abuffer tube.

SUMMARY

One embodiment of the disclosure relates to a crush resistant opticalcable. The cable includes a cable body including an inner surfacedefining a channel within the cable body. The cable includes a coreelement located in the channel of the cable body. The core elementincludes a tube including an outer surface, an inner surface and achannel defined by the inner surface of the tube. The tube includes afirst layer formed from a first material, and the first layer definesthe inner surface of the tube. The cable includes an optical fiberlocated within the channel of the tube. The first layer is formed from apolymer material having modulus of elasticity of less than 100 MPa suchthat the first layer acts as a compliant cushioning layer at leastpartially contacting and surrounding an outer surface of the opticalfiber when radially directed forces are applied to the outer surface ofthe tube.

An additional embodiment of the disclosure relates to an optical cable.The optical cable includes a cable body having an inner surface defininga channel within the cable body. The cable includes a plurality of tubeseach including an outer surface, an inner surface and a channel definedby the inner surface of the tube. Each tube includes a first layerformed from a first polymer material, and the first layer defines theinner surface of the tube. The cable includes a plurality of opticalfibers located within the channel of each tube. Each optical fiberincludes an optical core surrounded by cladding of a differentrefractive index than the optical core, and the cladding is surroundedby a fiber coating layer. The first polymer material has a modulus ofelasticity that is less than the modulus of elasticity of the materialof the fiber coating layer.

An additional embodiment of the disclosure relates to a crush resistantoptical fiber buffer tube. The buffer tube includes an outer surface, aninner surface, a channel defined by the inner surface, and a first layerformed from a first material. The first layer defines the inner surface.The buffer tube includes a plurality of optical fibers located withinthe channel. Each optical fiber includes an optical core surrounded bycladding of a different refractive index than the optical core, and thecladding is surrounded by a fiber coating layer. The first material hasa modulus of elasticity that is less than 100 MPa, and the modulus ofelasticity of the material of the fiber coating layer is greater than1000 MPa. A total radial thickness of the buffer tube between the innersurface and the outer surface is between 0.25 mm and 0.5 mm, and aradial thickness of the first layer is at least 30% of the total radialthickness of the buffer tube.

Another embodiment of the disclosure relates to an impact resistantoptical cable. The cable includes a cable body having an inner surfacedefining a channel within the cable body. The cable includes a coreelement located in the channel of the cable body. The core elementincludes a tube including an outer surface, an inner surface and achannel defined by the inner surface of the tube, and the tube includesa first layer formed from a polymer material, the first layer definingthe inner surface of the tube. The core element includes at least onecoated optical fiber located within the channel of the tube. The tube isconfigured such that an impact on the tube results in a force impartedby the tube on the at least one coated optical fiber corresponding tothe impaction parameter ρ (rho) of less than or equal to 2800 m⁻¹.

Another embodiment of the disclosure relates to an impact resistantoptical cable including a cable body including an inner surface defininga channel within the cable body. The cable includes a core elementlocated in the channel of the cable body. The core element includes atube having an outer surface, an inner surface and a channel defined bythe inner surface of the tube, and the tube has a first layer definingthe inner surface of the tube. The core element has at least one coatedoptical fiber located within the channel of the tube. The first layer isformed from a polymer material and includes a Maxwell element, and theresponse time of the Maxwell element of the polymer material of the tube(C₂/K₂) is less than or equal to 1 sec.

Another embodiment of the disclosure relates to an impact resistantoptical cable including a cable body including an inner surface defininga channel within the cable body. The cable includes a core elementlocated in the channel of the cable body. The core element includes atube having an outer surface, an inner surface and a channel defined bythe inner surface of the tube, and the tube has a first layer definingthe inner surface of the tube. The core element includes at least onecoated optical fiber located within the channel of the tube. The firstlayer is formed from a polymer material and includes a Kelvin element,and the response time of the Kelvin element of the tube material (C₁/K₁)is less than or equal to 1 sec.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an optical fiber cable according to anexemplary embodiment.

FIG. 2 is a perspective view of a core element of the cable of FIG. 1according to an exemplary embodiment.

FIG. 3 is a cross-sectional view of the buffer tube of FIG. 2 accordingto an exemplary embodiment.

FIG. 4 is a cross-sectional view of the buffer tube of FIG. 3 showingdeformation under radial loading according to an exemplary embodiment.

FIG. 5 is a cross-sectional view of an optical fiber of the core elementof FIG. 2 according to an exemplary embodiment.

FIG. 6 is a cross-sectional view of a buffer tube according to anotherexemplary embodiment.

FIG. 7 is a diagram of a model of an impact resistant buffer tube and acoated optical fiber under impact according to an exemplary embodiment.

FIG. 8 is a graph of select impact resistant buffer tube example modelsshowing the time response and force distribution of those buffer tubesunder impact compared to a standard polypropylene buffer tube.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of an opticalcommunication cable (e.g., a fiber optic cable, an optical fiber cable,etc.) and an optical fiber carrying tube are shown. In general, thecable embodiments disclosed herein include one or more optical fibercontaining core elements. In various embodiments, the optical fibercontaining core elements include a tube (e.g., a buffer tube)surrounding one or more optical transmission elements (e.g., opticalfiber) located within the tube. In general, the buffer tube acts toprotect the optical fibers under the wide variety of forces that thecable may experience during manufacture, installation, handling, in use,etc.

In particular, the forces the cable may experience include compressionloading experienced during or following installation (e.g., compressionbending, radial crush, etc.). For example, the cable may experiencerapid high force, short duration loading events (e.g., impact events),such as forces that impact the cable as the cable is being pulled aroundcorners, mandrels, shims, etc. during installation. During certaininstallation, these high force, short duration impacts occur repeatedlyat intervals along the length of the cable (which can be kilometers inlength) as the cable is run to the desired position for installation.Thus, it is believed that by providing a buffer tube formed from one ormore materials with elastic and/or viscous properties specificallyidentified as discussed herein, improved fiber protection with thebuffer tube can be achieved even under high force, short duration impactevents. Applicant has found that buffer tubes formed from materialshaving the properties discussed herein have a time response under shortduration or impact loading that allows the buffer tube totransfer/absorb energy from the impact event, and thereby protects theoptical fibers. For example, it is believed that by using the buffertube embodiments discussed herein to cushion optical fibers during crushor impact events, the optical fibers and the outer coating of opticalfibers, particularly at the fiber cross-overs, are protected, and damageis resisted or prevented which in turn may decrease the signalattenuation experienced within the optical fiber following the crush orimpact events.

In various embodiments disclosed herein, the buffer tubes include one ormore layer of a rubbery, compliant, elastic and/or viscoelastic materialthat acts to cushion the optical fibers within the tube during radial orcompression loading, such as short duration impact events. In theseembodiments, the compliant material of the buffer tube deforms andenvelops the optical fibers during loading protecting the opticalfibers. Because the material of the buffer tubes discussed herein haveresponse times to loading that allows the buffer tube to absorb and/ortransfers energy under short duration, impact loading, the buffer tubesdiscussed herein are particularly well suited to protecting opticalfibers from the impact events common during installation. Further, in atleast some embodiments, once the loading is removed the elastic buffertube material returns substantially to its original shape.

In at least some embodiments, the buffer tubes of the present disclosureutilize a material having a relatively low modulus of elasticity tocushion optical fibers rather than utilizing the relatively hardmaterials typical in conventional buffer tubes. In various embodiments,the elasticity and/or hardness of the compliant buffer tube material isselected to provide sufficient protection to optical fibers, while stillproviding sufficient structure for handling and processing during cablemanufacturing. Further, in some embodiments, the viscosity of thematerial of the buffer tube is selected to ensure sufficient timeresponse under short duration or impact loading such that the buffertube can transfer or absorb energy under such loading, therebyprotecting the optical fibers. In some embodiments, the buffer tubes areformed from a material having a combination of elasticity and viscositywithin specifically identified ranges (discussed herein) that Applicanthas identified as providing satisfactory protection to optical fibersfrom impact events. In addition, the thickness of the compliant layer ofthe buffer tube is selected to allow the compliant material to envelopand at least partially surround the optical fibers during compressionand/or under impact.

In specific embodiments, the compliant material of the buffer tube formsan inner, fiber contacting layer to provide cushioning during radialloading, and the buffer tube includes an outer more rigid layer locatedoutside of the inner fiber contacting layer. In various embodiments, theouter layer is substantially more rigid than the inner layer. In suchembodiments, the outer rigid layer provides structure during buffer tubestorage, buffer tube handling during cable construction, etc., and theinner layer provides protection to the fibers.

Referring to FIG. 1, an optical cable, shown as cable 10, is shownaccording to an exemplary embodiment. Cable 10 includes a cable body,shown as cable jacket 12, having an inner surface 14 that defines achannel, shown as central bore 16. A plurality of optical transmissionelements, shown as optical fibers 18, are located within bore 16. Invarious embodiments, the optical fibers 18 can include a wide variety ofoptical fibers including multi-mode fibers, single mode fibers, bendinsensitive fibers, multi-core optical fibers, etc. Generally, cable 10provides structure and protection to optical fibers 18 during and afterinstallation (e.g., protection during handling, protection fromelements, protection from vermin, etc.).

In the embodiment shown in FIG. 1, cable 10 includes a plurality of coreelements located within central bore 16. A first type of core element isan optical transmission core element, and these core elements includebundles of optical fibers 18 that are located within tubes, shown asbuffer tubes 20. One or more additional core elements, shown as fillerrods 22, may also be located within bore 16. Filler rods 22 and buffertubes 20 are arranged around an elongate rod, shown as central strengthmember 24, that is formed from a material such as glass-reinforcedplastic or metal (e.g., steel).

In the embodiment shown, filler rods 22 and buffer tubes 20 are shown ina helical stranding pattern, such as an SZ stranding pattern, aroundcentral strength member 24. Helically wound binders 26 are wrappedaround buffer tubes 20 and filler rods 22 to hold these elements inposition around strength member 24. In some embodiments, a thin-film,extruded sheath may be used in place of binders 26. A barrier material,such as water barrier 28, is located around the wrapped buffer tubes 20and filler rods 22. In various embodiments, cable 10 may include areinforcement sheet or layer, such as a corrugated armor layer, betweenlayer 28 and jacket 12, and in such embodiments, the armor layergenerally provides an additional layer of protection to optical fibers18 within cable 10, and may provide resistance against damage (e.g.,damage caused by contact or compression during installation, damage fromthe elements, damage from rodents, etc.). In some embodiments, designedfor indoor applications, cable 10 may include fire resistant materials,such as fire resistant materials embedded in jacket 12 and/or fireresistant intumescent particles located within channel 16.

Referring to FIG. 2, a buffer tube 20 and optical fibers 18 are shownaccording to an exemplary embodiment. Buffer tube 20 includes an outersurface 30 that defines the exterior surface of the buffer tube and aninner surface 32 that defines a channel, shown as central bore 34.Optical fibers 18 are located within central bore 34. In variousembodiments, optical fibers 18 may be loosely packed within buffer tube20 (e.g., a “loose buffer”), and in such embodiments, cable 10 is aloose tube cable. In various embodiments, central bore 34 may includeadditional materials, including water blocking materials, such as waterswellable gels.

In general, as noted above, in various embodiments, buffer tube 20includes at least one layer of compliant, rubbery, elastic orviscoelastic material that acts to cushion optical fibers 18 withinbuffer tube 20. In various embodiments, the compliant material of buffertube 20 is located such that it is the compliant material of buffer tube20 that defines inner surface 32. In this manner, the compliant materialforms the surface that directly contacts and engages optical fibers 18under compression, crush, impact or other radially directed forces abuffer tube may experience.

Referring to FIG. 3, a cross-sectional view of buffer tube 20 is shownaccording to an exemplary embodiment. In the embodiment of FIG. 3,buffer tube 20 is formed from a single layer of compliant polymermaterial. In this embodiment, buffer tube 20 is formed from asubstantially continuous and contiguous, single extruded polymer layerthat defines both outer surface 30 and inner surface 32 of buffer tube20. FIG. 3 generally shows buffer tube 20 in the relaxed state (e.g.,without substantial radial loading), and as can be seen, prior to radialloading, buffer tube 20 is a generally cylindrical tube.

Referring to FIG. 4, buffer tube 20 is shown under radial loading,represented by arrows 42. When buffer tube 20 experiences a crush event,impact, compression or other radial loading, represented schematicallyas force 42, the compliant material of buffer tube 20 deforms and atleast partially envelops optical fibers 18. Thus, under forces 42, innersurface 32 of buffer tube 20 engages at least a portion of outer fibersurface 40 and generally deforms conforming to the shape of opticalfibers 18. The deformation of tube 20 from the cylindrical shape shownin FIG. 3 to the elliptical shape of FIG. 4 may act to absorb some ofthe forces 42 experienced by buffer tube 20, and by enveloping opticalfibers 18, the compliant material of buffer tube 20 acts to transfer atleast a portion of forces 42 around optical fibers 18 rather thanimparting the forces entirely to fibers 18 which may otherwise causefiber damage. In addition, it is believed that compliant nature of thematerial of buffer tube 20 allows more room for the fibers during crushevents and dissipates external force due to the compliance of buffertube 20 even at high compression rates. As discussed in more detailbelow, Applicant has determined (via the modeling discussed below) thatin certain embodiments, forming buffer tube 20 from a viscoelasticmaterial with the identified ranges of elasticity and viscosity, buffertube 20 is able to envelop optical fibers 18 and dissipate energy evenduring short duration, high load, impact events of the sort experiencedduring installation. Because of the elastic nature of the material ofbuffer tube 20, once forces 42 are removed, buffer tube 20 returns tothe shape as generally shown in FIG. 3 with little or no permanentdeformation.

In various embodiments discussed herein, buffer tube 20 is structured byrelative sizing, by material type and/or by material properties toprotect optical fibers 18 during various types of radial loading. Forexample in various embodiments, buffer tube 20 is formed from acompliant, elastic material of sufficient strength and rigidity toprotect optical fibers 18 while also allowing buffer tubes 20 to bestored and handled during construction of an optical cable. In oneembodiment, buffer tube 20 is formed from a rubber like polymer that iscapable of recovering from large deformations quickly, and in a specificembodiment, buffer tube 20 is formed from a material that retractswithin 1 minute to less than 1.5 times its original length after beingstretched at room temperature to twice its length and held for 1 minutebefore release.

In various embodiments, buffer tube 20 is formed from a material havinga relatively low modulus of elasticity (e.g., as compared to thematerials typically used for buffer tube construction). In variousembodiments, buffer tube 20 is made from a material and specifically, apolymer material, having a modulus of elasticity of less than 200 MPa orhaving a modulus of elasticity of less than 100 MPa. In otherembodiments, buffer tube 20 is made from a polymer material having amodulus of elasticity of less than 30 MPa, specifically less than 10 MPaand more specifically less than 5 MPa. In various embodiments, buffertube 20 is formed from a linear material having a modulus of elasticityof less than 100 MPa. In various embodiments, each modulus of elasticityof the different materials discussed herein is the modulus in theelastic region of the material. In various embodiments, buffer tube 20is made from a material with a stress-strain multiplier below 0.5 (forexample for use of a non-linear material similar to polypropylene toform buffer tube 20). In various embodiments, it is believed based onvarious test data, that a buffer tube 20 formed from a material havingone or more of the physical properties discussed herein will protect thefiber (and fiber coating in particular) from damage even underrelatively high compression forces (e.g., 24 N per millimeter of fiberlength).

In various embodiments, buffer tube 20 is formed from a material havinga relatively low hardness (e.g., as compared to the materials typicallyused for buffer tube construction). In various embodiments, buffer tube20 is made from a material and specifically, a polymer material, havinga Shore hardness between 40A and 40D. In various embodiments, thematerial of buffer tube 20 has a low compression set and is extrudable.In various embodiments, buffer tube 20 is made from a material having acompression set of less 25% as determined by the test method defined inASTM D395.

In various embodiments, buffer tube 20 is formed from a material thatcan be deformed substantially while still returning to its originalshape with little or no permanent deformation. In various embodiments,the material of buffer tube 20 has a relatively high percent elongationat the yield point of the material. In various embodiments, the materialof buffer tube 20 has a percent elongation at the yield point of greaterthan 30%, specifically greater than 40% and more specifically of 50%.

In various embodiments, buffer tube 20 may be formed from a wide varietyof materials with physical properties as discussed herein. In variousembodiments, buffer tube 20 may be formed from an extrudable polymermaterial with physical properties as discussed herein. In variousembodiments, buffer tube 20 may be formed from a rubber-like polymermaterial having with physical properties as discussed herein. Inspecific embodiments, buffer tube 20 may be formed from a thermoplasticelastomer material or a thermoplastic urethane material. Themorphological differences between thermoplastic elastomers and thermosetrubbers, copolymers with rubbery phases or other materials with highelongation are the presence of soft rubbery phases or blocks bonded intohard plastic domains or blocks with distinct melting points. This allowsthermoplastic elastomers to be processed using conventionalthermoplastic methods and equipment such as extrusion or injectionmolding. The thermoplastic elastomers behave like a vulcanized rubber upuntil the point where external stress is applied past the strain pointfor permanent deformation (due to loss of bonding between hard and softblocks). Thus, it is believed for at least these reasons, variousthermoplastic elastomer materials, as discussed herein, have suitablephysical characteristics for protecting optical fibers 18 during crushevents.

In a specific embodiment, buffer tube 20 may be formed from anelastomeric PVC material. In various embodiments, the polymer materialof buffer tube 20 may be a thermoplastic elastomer material from thefollowing polymer classes: block copolymers, thermoplastic olefins, suchas Vistaflex and Telcar, elastomeric alloys, such as Santoprene andAlcryn, polyamides, such as Pebax and Vestamid, polyurethanes, such asTexin and Pellethane, copolyesters, such as Arnitel or Hytrel, orstyrenics, such as Kraton and Finneprene. In other embodiments, buffertube 20 may be formed from any class of thermoplastic elastomer materialhaving one or more of the physical properties discussed herein.

In various embodiments, buffer tube 20 is sized to provide sufficientprotection to optical fibers 18. In general, by utilizing a cushioning,elastic material for buffer tube 20, buffer tubes 20 may be thinnerand/or smaller than is typical while maintaining sufficientcrush-performance. In the embodiment shown in FIG. 3, buffer tube 20 hasa thickness shown as T1, an outer diameter, shown as OD1, and an innerdiameter, shown as ID1. In various embodiments, prior to distortionunder radial forces, T1 of buffer tube 20 is between 0.25 mm and 0.5 mm,specifically between 0.3 mm and 0.4 mm and more specifically about 0.35mm (e.g., 0.35 mm plus or minus 0.01 mm). In some embodiments, prior todistortion under radial forces, T1 of buffer tube 20 is less than 0.75mm, specifically between 0.1 mm and 0.75 mm, more specifically between0.4 mm and 0.6 mm and even more specifically about 0.5 mm (e.g., 0.5 mmplus or minus 0.01 mm). As shown in FIG. 3, prior to distortion underradial forces, OD1 of buffer tube 20 is between 1.5 mm and 3.5 mm,specifically between 1.8 mm and 2.4 mm, and more specifically is between2 mm and 2.25 mm. In addition, prior to distortion under radial forces,ID1 of buffer tube 20 is between 1.2 mm and 1.9 mm, specifically between1.5 mm and 1.7 mm and more specifically between 1.55 mm and 1.6 mm.

In various embodiments, the thickness T1 of buffer tube 20 and/or themodulus of elasticity of the cushioning material of buffer tube 20 maybe described relative to the size and material properties of opticalfibers 18. Referring to FIG. 5, an exemplary embodiment of an opticalfiber 18 is shown. In various embodiments, each optical fiber 18 has anoptical core 60 surrounded by a cladding layer 62 that may be formedfrom one or more layers of cladding material. Cladding layer 62 has adifferent refractive index than optical core 60 and helps guide lightdown optical core 60 of the optical fibers by total internal reflection.In addition each optical fiber 18 includes at least one polymer fibercoating layer 64 surrounding cladding layer 62. In various embodiments,each optical fiber 18 has a fiber radius, shown as FR, that is theradial distance from the center point of optical core 60 to an outermost surface of fiber coating layer 64. In various embodiments, FR ofoptical fiber 18 is between 75 micrometers and 175 micrometers,specifically between 100 micrometers and 140 micrometers and morespecifically about 121 micrometers (e.g., 121 micrometers plus or minus1%). In various embodiments, polymer fiber coating layer 64 may be a UVcured polymer material such as an acrylate material. In a specificembodiment, optical fiber 18 is 242 micrometer diameter CPC6i availablefrom Corning, Inc. coated fiber.

In various embodiments, T1 of buffer tube 20 is selected such thatbuffer tube 20 provides sufficient cushioning to optical fibers 18 underradial loading. In one embodiment, T1 of buffer tube 20 is greater thanFR such that buffer tube 20 is permitted to substantially or completelyenvelop fibers 18 under loading. In various embodiments, T1 is at least1.5 times FR, is at least 2 times FR, at least 5 times FR and at leastthan 10 times FR. In a specific embodiment, T1 is greater than 1.5 timesthe diameter of optical fiber 18, and more specifically is greater than2 times the diameter of optical fiber 18.

As noted above, optical fiber 18 may include polymer fiber coating layer64 located toward the outside of the cladding layer surrounding theoptical core. In various embodiments, the material of buffer tube 20 hasa modulus of elasticity that is lower than the polymer fiber coating. Invarious embodiments, the polymer fiber coating layer 64 has a modulus ofelasticity greater than 500 MPa, specifically greater than 1000 MPa andmore specifically greater than 1500 MPa. In specific embodiments, thepolymer fiber coating layer 64 includes an inner layer of materialhaving a low modulus of elasticity (e.g., less than 5 MPa, less than 0.5MPa) and an outer layer of material having a high modulus of elasticity(e.g., greater than 500 MPa, greater than 1000 MPa, greater than 1500MPa).

Referring to FIG. 3, as noted above, optical fibers 18 are generallyloosely packed within buffer tube 20 (e.g., a “loose buffer”). In suchembodiments, the cross-sectional area of buffer tube channel 34 issubstantially larger than the cross-sectional area occupied by fibers 18within tube 20. In various embodiments, the cross-sectional area ofbuffer tube channel 34 is at least twice the size of the cross-sectionalarea occupied by fibers 18 within tube 20. Thus, in contrast to anoptical fiber ribbon design, buffer tube 20 utilizes a compliant polymerbuffer tube 20 while at the same time providing optical fibers looselywithin the buffer tube.

Referring to FIG. 6, a buffer tube 50 is shown according to anotherexemplary embodiment. Buffer tube 50 is substantially the same as buffertube 20 except as discussed herein. In contrast to buffer tube 20,buffer tube 50 has multiple layers of material forming buffer tube 50.In the embodiment shown, buffer tube 50 has a first layer, shown asinner layer 52, and a second layer, shown as outer layer 54. In thisembodiment, inner layer 52 includes an inner surface that defines buffertube inner surface 32, and outer layer 54 includes an outer surface thatdefines buffer tube outer surface 30. As shown, inner layer 52 is asubstantially contiguous and continuous layer of material surroundingoptical fibers 18, and outer layer 54 is a substantially contiguous andcontinuous layer of material located outside of and surrounding innerlayer 52. In the two-layer embodiment of FIG. 6, inner layer 52 andouter layer 54 combined define the radial thickness of buffer tube 50which is the same as T1 of buffer tube 20 discussed above.

In general, because inner layer 52 defines the inner surface of buffertube 50 and will contact optical fibers 18 under loading, inner layer 52is formed from any of the compliant, elastic and protective materialsdiscussed above regarding buffer tube 20. In such embodiments, outerlayer 54 may be made from a relatively hard and inelastic material ascompared to inner layer 52. In such embodiments, inner layer 52 providesthe crush protection to optical fibers 18 while outer layer 54 providesstructure and rigidity to facilitate storage and handling of buffer tube50. It should be understood that in other embodiments, buffer tube 50may include more than two layers, and in such embodiments, the innermost layer is a cushioning elastic layer similar to inner layer 52discussed herein.

In various embodiments, outer layer 54 is formed from an extrudablepolymer material. In various embodiments, outer layer 54 is made from amaterial and specifically, a polymer material, having a modulus ofelasticity of greater than 500 MPa. In other embodiments, outer layer 54is made from a polymer material having a modulus of elasticity ofgreater than 1000 MPa. Thus, in various embodiments, outer layer 54 maybe made from a material having a modulus of elasticity that is 10 timesgreater than the modulus of inner layer 52, that is 50 times greaterthan the modulus of inner layer 52, that is 100 times greater than themodulus of inner layer 52 or that is 200 times greater than the modulusof inner layer 52. In various embodiments, inner layer 52 and outerlayer 54 may be coextruded layers.

In various embodiments, outer layer 54 may also be formed from amaterial that is harder than the material of inner layer 52. In variousembodiments, the material of outer layer 54 has a Rockwell hardnessgreater than or equal to 80.

In various embodiments, outer layer 54 may be made from any polymersuitable for buffer tube construction having the physical propertiesdiscussed above. In one embodiment, outer layer 54 is formed from apolypropylene material. In another embodiment, outer layer 54 is formedfrom a polycarbonate (PC) material. In other embodiments, outer layer 54is formed from one or more polymer material including polybutyleneterephthalate (PBT), polyamide (PA), polyoxymethylene (POM),poly(ethene-co-tetrafluoroethene) (ETFE), etc. In various embodiments,inner layer 52 is formed from a material that forms a bond with thematerial of outer layer 54 during coextrusion. In embodiments in whichouter layer 54 is a polyolefin, such as polypropylene, inner layer 52may be formed from a thermoplastic olefin material or an elastomericalloy material to facilitate bonding during coextrusion.

Referring to FIG. 6, inner layer 52 has a thickness in the radialdirection, shown as T2, and outer layer 54 has a thickness in the radialdirection, shown as T3. As noted above, T2 and T3 together account forthe total thickness, T1, as discussed above. In various embodiments, T2is greater than or equal to T3. In various embodiments, T2 is at least30% of T1. In various embodiments, T2 is between 30% and 90% of T1. In aspecific embodiment, T2 and T3 are substantially equal (e.g., within 10%of each other).

In various embodiments, T2 is selected to provide sufficient protectionto optical fibers 18. In one embodiment, T2 is greater than FR ofoptical fibers 18 such that inner layer 52 of buffer tube 50 ispermitted to substantially or completely envelop fibers 18 underloading. In various embodiments, T2 is at least 2 times FR, at least 5times FR and at least 10 times FR.

Referring back to FIG. 1, in various embodiments, cable jacket 12 may beformed from multiple layers similar to buffer tube 50. In a specificembodiment, cable jacket 12 may have an inner layer that defines innersurface 14 and an outer layer that defines the outer surface of cablejacket 12. In one such embodiment, the inner layer of cable jacket 12 isformed from the same material as inner layer 52 of buffer tube 50, andthe outer layer of cable jacket 12 is formed from the same material asouter layer 54 of buffer tube 50. In such embodiments, the multilayercable jacket 12 provides additional crush resistance to cable 10.

In various embodiments, cable jacket 12 may be a made from a widevariety of materials used in cable manufacturing such as medium densitypolyethylene, polyvinyl chloride (PVC), polyvinylidene difluoride(PVDF), nylon, polyester or polycarbonate and their copolymers. Inaddition, the material of cable jacket 12 may include small quantitiesof other materials or fillers that provide different properties to thematerial of cable jacket 12. For example, the material of cable jacket12 may include materials that provide for coloring, UV/light blocking(e.g., carbon black), burn resistance, etc.

Referring to FIGS. 7 and 8, in various embodiments, buffer tube 20 andor buffer tube 50 may be configured (e.g., through selection ofthickness, materials with particularly material properties, externalshapes, shapes of internal channel shape, etc.) to protect opticalfibers 18 from damage under impact loading (e.g., short duration, highforce loading). In such embodiments, the behavior of the buffer tubeunder impact, and specifically how the buffer tube transfers the impactforce to the optical fibers can be modeled as shown in FIG. 7, and theproperties of a buffer tube meeting various impact performanceparameters can be selected in accordance with the modeling. Similarly,it can be determined, through testing in accordance with the model,whether a given buffer tube design (e.g., a buffer tube of particularsize, shape, thickness, material, etc.) includes one or more of themodeled elements with one or more of the performance parametersdiscussed below (e.g., impaction factor, response time of modeledMaxwell element, response time of modeled Kelvin element, etc.).

The viscoelastic and creep behavior of buffer tubes under an impact loadhas been modeled using the system 100 illustrated in FIG. 7. Theimpactor 102 has a mass M₁ and impacts the buffer tube 20 with avelocity V₀. The cushioning effect of buffer tube 20 has been modeled byconsidering buffer tube of thickness, δ (delta), and mass M₂ as aBurgers material having a Kelvin element 104 and a Maxwell element 106in series. As will be generally understood, Kelvin element 104 describesthe properties and the behavior of a cushioning buffer tube in responseto an impact when the buffer tube is in the creep deformation region,and Maxwell element 106 describes the properties and the behavior of acushioning buffer tube in response to an impact when the buffer tube isin the elastic deformation region.

The Kelvin element 104 is described as comprised of a spring 108 and adashpot 110 (also referred to herein as a dampener and or shockabsorber) in parallel. The Kelvin element spring 108 has a springconstant, K₁ equal to the modulus of elasticity of the Kelvin element ofthe buffer tube material in the creep deformation region, and thedashpot 110 of the Kelvin element 104 has a dashpot constant C₁ equal tothe viscosity of the Kelvin element of the buffer tube material in thecreep deformation region.

The Maxwell element 106 is described as comprised of a spring 112 and adashpot 114 in series. The Maxwell element spring 112 has a springconstant K₂ equal to the modulus of elasticity of the Maxwell element ofthe buffer tube material in the elastic region, and the Maxwell elementdashpot 114 has a dashpot constant C₂ equal to the viscosity of theMaxwell element of the buffer tube material in the plastic deformationregion. It should be understood that FIG. 7 describes the behavior of asingle layer buffer tube such as buffer tube 20. However, a modeldescribing a multilayer buffer tube, such as buffer tube 50, willinclude additional sets of Kelvin and Maxwell elements (similar toelements 104 and 106) for each additional material layer of the buffertube.

The overall mass of coated optical fibers 18 and surfaces beingcushioned by the buffer tubes is M₃. The viscoelastic behavior of thecoated optical fiber(s) 18 has been modeled by considering the coatedoptical fiber(s) within buffer tube 20 as a Kelvin element 116 having aspring 118 and dashpot 120 in parallel. The optical fiber Kelvin elementspring 118 has a spring constant K₃ equal to the modulus of elasticityof the Kelvin element of the coated optical fiber(s) in the viscoelasticregion, and the optical fiber Kelvin element dashpot has a dashpotconstant, C₃, equal to the viscosity of the Kelvin element of the coatedoptical fiber in the viscoelastic region.

The terms x1 and x2 refer to the displacement of M₂ and M₃ from theirinitial positions, respectively. It is understood that the spring anddashpots constants for the Kelvin and Maxwell elements of the buffertube material and for the Kelvin element of the coated optical fiber canbe determined by one skill in the art by analyzing the creep andviscoelastic response of the particular materials used to form a givenbuffer tube or coated optical fiber, for example using tensile testingor DMA for measuring properties as a function of shear rate. The coatedoptical fibers in the examples shown below include a glass core andglass cladding that together has an outer diameter of glass of 125microns and an optical fiber polymer coating that has an outer diameterof about 250 microns. Additional examples utilize an optical fiberpolymer coating having an outer diameter of about 200 microns.

Using the representative system model 100 as shown in FIG. 7,deformation of buffer tube, force imparted by the buffer tube on thecoated optical fibers and the energy absorbed by the buffer tube can becalculated, based on various buffer tube and optical fiberconfigurations. In various embodiments, the choice of material forbuffer tube 20 acts to protect optical fiber(s) 18 by reducing theforce, F, imparted by buffer tube 20 onto the coated fiber(s) 18 as aresult of the impact from impactor 102 on buffer tube 20. The cushioningeffect (e.g., the force reduction) provided by buffer tube 20 is relatedto the impaction factor, ρ (rho), which is set forth in Equation 1below, for a buffer tube of a given thickness:

$\begin{matrix}{\rho = \frac{F}{M_{1}V_{0}^{2}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Tables 1A-1C below provide the output of system model 100 for variousexamples of cushioning buffer tubes 20, based on different values of K₁,K₂, K₃, C₁, C₂, and C₃. As will be understood, based on the informationin Tables 1A-1C, a person of skill in the art can configure a cushioningbuffer tube (e.g., through design/selection of materials, buffer tubesize, shape, etc.) to provide specific and selected impact performancerepresented by ρ (rho) and/or various time responses for the differentmodeled elements of the buffer tube as shown in the tables below. Table2 below provides comparative examples of buffer tubes formed fromconventional buffer tube materials. As shown in Tables 1 and 2 below,system model 100 is used to determine the impaction parameter ρ forbuffer tube materials having different combinations of Kelvin element104 and Maxwell element 106 parameters K₁ and K₂ {reported in units ofPascal (Pa [10⁻⁶ MPa])} and C₁ and C₂ {reported in units of Pascalseconds (Pa·s [10⁻⁶ MPa·s])}. The tables also show the response timesfor the different modeled elements of buffer tube examples havingdifferent combinations of Kelvin element 104 and Maxwell element 106parameters K₁, K₂, C₁ and C₂. The tables also show the modulus of theKelvin element 116 of the coated optical fiber(s) 18 in thevisco-elastic region, K₃, in Pa, as well as viscosity of the Kelvinelement of the coated optical fiber(s) 18 in the visco-elastic region,C₃, in Pa·s. The data in tables 1 and 2 below is modeled for materialsat room temperature (e.g., about 20-25 degrees C.).

TABLE 1A Cushioning Buffer Tube Examples Viscosity of the Viscosity ofthe Viscosity of the Kelvin Maxwell element of Kelvin element ofCushioning Buffer tube element of the buffer the buffer tube the coatedoptical Buffer wall tube material in the creep material in the elasticfibers in the visco- Tube thickness, deformation region, C1, deformationregion, elastic region, C3, Examples cm Pa · s C2, Pa · s Pa · s 1 0.054.00E+03 6.00E+03 1.00E+07 2 0.05 4.00E+03 6.00E+03 1.00E+07 3 0.051.60E+04 2.40E+04 1.00E+07 4 0.05 3.60E+04 5.40E+04 1.00E+07 5 0.054.00E+05 6.00E+05 1.00E+07 6 0.05 4.20E+07 1.21E+09 1.00E+07 7 0.054.20E+06 1.21E+08 1.00E+07 8 0.05 1.00E+08 1.00E+08 1.00E+07 9 0.051.00E+07 1.00E+07 1.00E+07 10 0.05 1.00E+06 1.00E+06 1.00E+07 11 0.051.00E+05 1.00E+05 1.00E+07 12 0.05 1.00E+04 1.00E+04 1.00E+07 13 0.051.00E+08 1.00E+08 1.00E+07 14 0.05 1.00E+07 1.00E+07 1.00E+07 15 0.051.00E+06 1.00E+06 1.00E+07 16 0.05 1.00E+05 1.00E+05 1.00E+07 17 0.051.00E+04 1.00E+04 1.00E+07

TABLE 1B Cushioning Buffer Tube Examples Modulus of the Maxwell Modulusof the Kelvin element of the buffer Modulus of the Kelvin Cushioningelement of the buffer tube tube material in the element of the coatedBuffer Tube material in the creep elastic deformation optical fibers inthe visco- Examples deformation region, K1, Pa region, K2, Pa elasticregion, K3, Pa 1 1.00E+07 1.00E+07 5.00E+07 2 2.00E+07 2.00E+07 5.00E+073 4.00E+07 4.00E+07 5.00E+07 4 6.00E+07 6.00E+07 5.00E+07 5 2.00E+072.00E+08 5.00E+07 6 6.37E+08 1.22E+08 5.00E+07 7 6.37E+08 1.22E+085.00E+07 8 1.00E+08 1.00E+08 5.00E+07 9 1.00E+08 1.00E+08 5.00E+07 101.00E+08 1.00E+08 5.00E+07 11 1.00E+08 1.00E+08 5.00E+07 12 1.00E+081.00E+08 5.00E+07 13 1.00E+07 1.00E+07 5.00E+07 14 1.00E+07 1.00E+075.00E+07 15 1.00E+07 1.00E+07 5.00E+07 16 1.00E+07 1.00E+07 5.00E+07 171.00E+07 1.00E+07 5.00E+07

TABLE 1C Cushioning Buffer Tube Examples Maximum φ [=Force Maximum ρ[=Force that buffer tube that buffer tube Response time of imparts tocoated imparts to coated Response time of Maxwell element optical fibers· Padding optical Cushioning Kelvin element of the of the buffer tubeThickness/Impactor fibers/Impactor Buffer buffer tube material,material, C2/K2, Mass/(Impactor Mass/(Impactor Tube C1/K1, secondsseconds Velocity²)] Velocity²)], 1/m 1 0.0004 0.0006 0.17 342 2 0.00020.0003 0.21 420 3 0.0004 0.0006 0.43 860 4 0.0006 0.0009 0.62 1240 50.0020 0.0030 1.37 2740 6 0.0659 9.93 1.12 2240 7 0.0066 0.99 1.10 22008 1.0000 1.00 1.01 2020 9 0.1000 0.10 1.01 2016 10 0.0100 0.01 0.99 198811 0.0010 0.001 0.87 1748 12 0.0001 0.0001 0.43 858 13 10.0 10.0 0.32638 14 1.0000 1.00 0.32 638 15 0.1000 0.10 0.32 636 16 0.0100 0.01 0.30608 17 0.0010 0.001 0.22 432

TABLE 2A Comparative Buffer Tube Examples Viscosity of the Viscosity ofthe Viscosity of the Kelvin element of the Maxwell element of Kelvinelement of buffer tube material the buffer tube the coated opticalComparative in the creep material in the elastic fibers in the BufferTube Buffer tube wall deformation region, deformation region,visco-elastic Examples thickness, cm C1, Pa · s C2, Pa · s region, C3,Pa · s 1-Polypropylene 0.05 4.20E+08 1.21E+10 1.00E+07 2-PBT-PTMG 0.054.20E+08 1.21E+10 1.00E+07 copolymer

TABLE 2B Comparative Buffer Tube Examples Modulus of the Kelvin Modulusof the Maxwell element of the buffer tube element of the buffer Modulusof the Kelvin Comparative material in the creep tube material in theelement of the coated Buffer Tube deformation region, K1, elasticdeformation optical fibers in the visco- Examples Pa region, K2, Paelastic region, K3, Pa 1-Polypropylene 6.37E+09 1.22E+09 5.00E+072-PBT-PTMG 1.27E+09 2.44E+08 5.00E+07 copolymer

TABLE 2C Comparative Buffer Tube Examples Maximum Maximum φ [=Force ρ[=Force that that buffer tube buffer tube Response time of imparts tocoated imparts to Kelvin element Response time of optical fibers ·Padding coated optical Comparative of the buffer tube Maxwell element ofthe Thickness/Impactor fibers/Impactor Buffer Tube material, C1/K1,buffer tube material, Mass/(Impactor Mass/(Impactor Examples secondsC2/K2, seconds Velocity²)] Velocity²)], 1/m 1-Polypropylene 0.066 9.9263.53 7060 2-PBT-PTMG 0.330 49.63 1.58 3160 copolymer

As can been seen from a comparison of Table 1C and Table 2C, theresponse times of the Kelvin element, the Maxwell elements and/or theimpaction factor, ρ (rho), for many of the different cushioning buffertube examples are substantially less than the comparative buffer tubesformed from standard buffer tube materials. FIG. 8 shows a plot of φ(phi) for select buffer tube examples as well as for the polypropylenecomparative example versus ((time×impact velocity)/padding layerthickness). It should be noted in the tables above and FIG. 8, paddingthickness is the buffer tube wall thickness. Applicant believes that, atleast in some embodiments, the identified response times and impactionfactor are related to ability of the buffer tube to protect the opticalfibers 18 under crush events, and particularly under short duration,high load events, such as impact events experienced during the differentinstallation processes discussed above. It should be understood that thedata in the tables above is based on a buffer tube having a wallthickness of 0.05 cm.

Thus, in some embodiments, buffer tubes 20 are configured such that theimpact on the buffer tube results in a force F imparted by the buffertube on the coated optical fibers corresponding to the impactionparameter ρ of less than or equal to 2800 m⁻¹. In some otherembodiments, buffer tubes 20 are configured such that the impact on thebuffer tube results in a force F imparted by the buffer tube on thecoated optical fibers corresponding to the impaction parameter ρ of lessthan or equal to 1000 m⁻¹. In still other embodiments, buffer tubes 20are configured such that the impact on the buffer tube results in aforce F imparted by the buffer tube on the coated optical fiberscorresponding to the impaction parameter ρ of less than or equal to 500m⁻¹.

In still other embodiments yet, buffer tubes 20 are configured such thatthe impact on the buffer tube results in a force F imparted by thebuffer tube on the coated optical fibers corresponding to the impactionparameter ρ of greater than or equal to 100 m⁻¹, specifically 100m⁻¹≦ρ≦2800 m⁻¹, and more specifically 100 m⁻¹≦ρ≦1000 m⁻¹.

In some embodiments, the modulus of elasticity of the material of buffertube 20 in the elastic region (K₂) is less than or equal to 200 MPa. Insome other embodiments, the modulus of elasticity of the material ofbuffer tube 20 in the elastic region (K₂) is less than or equal to 100MPa. In still other embodiments, the modulus of elasticity of thematerial of buffer tube 20 in the elastic region (K₂) is less than orequal to 50 MPa. In still other embodiments yet, the modulus ofelasticity of the material of buffer tube 20 in the elastic region (K₂)is greater than or equal to 10 MPa. In some embodiments, the modulus ofelasticity of the material of buffer tube 20 falls within the range 10MPa≦K₂≦150 MPa, and specifically in the range 10 MPa≦K₂≦50 MPa.

In some embodiments, the response time of the Maxwell element of thematerial of buffer tube 20 (C₂/K₂) is less than or equal to 1 sec. Insome other embodiments, the response time of the Maxwell element of thematerial of buffer tube 20 (C₂/K₂) is less than or equal to 0.1 sec. Instill other embodiments, the response time of the Maxwell element of thematerial of buffer tube 20 (C₂/K₂) is less than or equal to 0.01 sec. Instill other embodiments yet, the response time of the Maxwell element ofthe material of buffer tube 20 (C₂/K₂) is less than or equal to 0.001sec. In still other embodiments yet, the response time of the Maxwellelement of the material of buffer tube 20 (C₂/K₂) is less than or equalto 0.0001 sec, specifically is 0.0001 sec.≦C₂/K₂≦1 sec, and morespecifically is 0.0001 sec.≦C₂/K₂≦0.01 sec.

In some embodiments, the response time of the Kelvin element of thematerial of buffer tube 20 (C₁/K₁) is less than or equal to 1 sec. Insome other embodiments, the response time of the Kelvin element of thematerial of buffer tube 20 (C₁/K₁) is less than or equal to 0.1 sec. Instill other embodiments, the response time of the Kelvin element of thematerial of buffer tube 20 (C₁/K₁) is less than 0.01 sec. In still otherembodiments yet, the response time of the Kelvin element of the materialof buffer tube 20 (C₁/K₁) is less than or equal to 0.001 sec. In stillother embodiments yet, the response time of the Kelvin element of thematerial of buffer tube 20 (C₁/K₁) is less than or equal to 0.0001 sec,specifically is 0.0001 sec.≦C₁/K₁≦1 sec, and more specifically is 0.0001sec.≦C₁/K₁≦0.01 sec. In various embodiments, buffer tubes 20 may beformed from materials having any combination or sub-combination ofproperties (e.g., thickness, modulus of elasticity, hardness, Maxwellresponse time, Kelvin response time, impaction factor, etc.) discussedherein.

FIG. 8 is a graph for several of the examples from Tables 1 and 2 ofForce×Padding Thickness/Mass of Impacting Body/(Impact Velocity²) as afunction of (Time×Impact Velocity)/Padding Layer Thickness. The resultsare plotted for the first cycle of impact of buffer tube on the coatedfiber and shows the maximum φ (phy)=ρ*padding thickness is less than 2(about 0.2 to about 1.4) for the select cushioned buffer tube examplesshown, and in contrast, the maximum 4) for the comparative examplepolypropylene buffer tube is greater than 3 (3.53). The results alsoshow that the select cushioned buffer tube examples shown alsodistribute the force over a broader time scale (better force dampening)and are significantly better than the comparative polypropylene andPBT-PTMG examples.

While the specific cable embodiments discussed herein and shown in thefigures relate primarily to cables and core elements that have asubstantially circular cross-sectional shape defining substantiallycylindrical internal lumens, in other embodiments, the cables and coreelements discussed herein may have any number of cross-section shapes.For example, in various embodiments, the cable jacket and/or buffertubes may have a square, rectangular, triangular or other polygonalcross-sectional shape. In such embodiments, the passage or lumen of thecable or buffer tube may be the same shape or different shape than theshape of the cable jacket and/or buffer tubes. In some embodiments, thecable jacket and/or buffer tubes may define more than one channel orpassage. In such embodiments, the multiple channels may be of the samesize and shape as each other or may each have different sizes or shapes.

The optical fibers discussed herein may be flexible, transparent opticalfibers made of glass or plastic. The fibers may function as a waveguideto transmit light between the two ends of the optical fiber. Opticalfibers may include a transparent core surrounded by a transparentcladding material with a lower index of refraction. Light may be kept inthe core by total internal reflection. Glass optical fibers may comprisesilica, but some other materials such as fluorozirconate,fluoroaluminate, and chalcogenide glasses, as well as crystallinematerials, such as sapphire, may be used. The light may be guided downthe core of the optical fibers by an optical cladding with a lowerrefractive index that traps light in the core through total internalreflection. The cladding may be coated by a buffer and/or anothercoating(s) that protects it from moisture and/or physical damage. Thesecoatings may be UV-cured urethane acrylate composite materials appliedto the outside of the optical fiber during the drawing process. Thecoatings may protect the strands of glass fiber.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein thearticle “a” is intended include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modificationscombinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An optical cable comprising: a cable bodyincluding an inner surface defining a channel within the cable body; anda plurality of tubes each including an outer surface, an inner surfaceand a channel defined by the inner surface of the tube, wherein eachtube includes a first layer formed from a first polymer material, thefirst layer defining the inner surface of the tube; and a plurality ofoptical fibers located within the channel of each tube, wherein eachoptical fiber includes an optical core surrounded by cladding of adifferent refractive index than the optical core, the claddingsurrounded by a fiber coating layer, and wherein each optical fiber hasfiber radius defined from a center point of the optical core to an outersurface of the fiber coating layer, wherein a thickness of the firstlayer of each of the plurality of tubes in the radial direction isgreater than the fiber radius; wherein the modulus of elasticity of thefirst material of each of the plurality of tubes is a modulus in theelastic region and is less than 30 MPa, and wherein the fiber coatinglayer includes an inner coating layer that has a modulus of elasticityin the elastic region of less than 5 MPa and an outer coating layer thathas modulus of elasticity in the elastic region greater than 1000 MPa,wherein the channel of each of the plurality of tubes has across-sectional area, wherein the cross-sectional area of the channel ofeach of the tubes is at least twice a total cross-sectional area of allof the plurality of optical fibers located within each of the tubes. 2.The optical cable of claim 1 wherein each of the plurality of tubesfurther includes a second layer formed from a second material, locatedaround and outside of the first layer, wherein the second material has amodulus of elasticity at least 10 times greater than the modulus ofelasticity of the first layer.
 3. The optical cable of claim 2 whereinthe modulus of elasticity of the first material of each of the pluralityof tubes is less than 30 MPa, wherein the modulus of elasticity of thesecond material of each of the plurality of tubes is greater than 500Mpa, wherein a radial thickness of the first layer is equal to orgreater than a radial thickness of the second material.
 4. The opticalcable of claim 3 wherein a radial thickness between inner and outersurfaces of each tube is between 0.25 mm and 0.5 mm.
 5. The opticalcable of claim 3 wherein the first material of the first layer is atleast one of a thermoplastic olefin, a thermoplastic urethane, athermoplastic copolyester and a thermoplastic polyamide, wherein thesecond material of the second layer is polypropylene, wherein materialof the fiber coating layer is a UV cured polymer layer.